The present embodiments relate to a radiation therapy system for irradiating a target volume that may change position and/or shape over time.
Radiation therapy may use high-energy photons or particles. U.S. Pat. No. 6,687,330 B2 discloses radiation therapy that uses high-energy photons. A particle therapy system typically has an accelerator unit and a high-energy beam guidance system. A synchrotron or cyclotron may be used to accelerate the particles, such as protons or carbon or oxygen ions.
The high-energy beam transporting system transports the particles from the accelerator unit to one or more treatment rooms. A distinction is made between “fixed beam” treatment rooms and gantry-based treatment rooms. Particles arrive at the treatment site from a fixed direction in “fixed beam” treatment rooms. In a gantry-based treatment room, the particle beam may be aimed at the patient from various directions using a gantry.
A distinction may also be made between scanning and scattering. Scattering employs a large-area beam adapted to the dimensions of the volume to be irradiated Scanning scans a “pencil beam” with a diameter of a few millimeters to centimeters over the volume to be irradiated. When a scanning system is embodied as a grid scanning system, the particle beam is steered “point by point” to a volume element of a grid until such time as a previously defined number of particles has been applied. The volume elements in the scanning area are irradiated in succession; preferably, the expanse of the “pencil beams” that are side by side overlap. The particles for one volume element contribute to the dose within this volume element and along the entire path struck by the particles.
A monitoring and safety system of the particle therapy system may be used to direct a particle beam, characterized by the parameters wanted, into the appropriate treatment room. The parameters of a radiation treatment procedure, for example, in a treatment plan, are summarized as an irradiation field. The irradiation field includes an association of the particle with the volume element. The irradiation filed is defined by how many particles from which direction and with what energy, are supposed to strike the patient or the volume elements. The energy of the particles determines the penetration depth into the patient. For example, the energy of the particles may determine the site at which the maximum interaction with the tissue takes place in the particle therapy. The energy of the particles defines the site where the maximum dose is deposited. During the treatment, the maximum deposited dose is located inside the tumor (or in the case of other medical applications of the particle beam, in the particle target area).
The monitoring and safety system controls a positioning device, with which the patient is positioned relative to the particle beam. For carrying out the treatment plan, the patient should assume a position for the irradiation that matches the planning. Matching the position to the plan is done, for example, by 2D position verification. 2D position verification includes, for example, before the irradiation is performed, calibrating 2D images with images from the irradiation planning.
European Patent Disclosure EP 0 986 070 and “The 200-MeV Proton Therapy Project at the Paul Scherrer Institute: Conceptual Design and Practical Realization”, E. Pedroni et al, Med. Phys. 22, 37-53 (1995) disclose particle therapy systems with a scanning system.
When planning a treatment, typically a plurality of irradiation fields, with different angles of incidence, are planned for individually. Each irradiation field is adapted to the scanning system. For example, each field is planned individually and its expanse is limited by a scanning range of the scanning system. The maximum deflection of the particle beam determines the scanning range. A distinction is made between 2D scanning (the particle beam deflection is in two directions) and 1D scanning. In 1D scanning, the patient is moved in increments, so that even a volume that is extensive in the second dimension can be irradiated.
Irradiation of a target volume in the radiation treatment phase may have a different position and/or size than was determined in the planning phase for setting up the irradiation field. This may be problematic because as a result of the change in location and/or size of the target volume, the target volume may not be located at the planned site in the patient despite position verification of the patient.
A similar situation arises in irradiation of targets that, for example, move because of respiration. These problems are discussed, for example, in E. Rietzel et al, “Four-Dimensional Image Based Treatment Planning: target volume segmentation and dose calculation in the presence of respiratory motion”, Int. J. Radiation Oncology Biol. Phys. Vol. 61, No. 5, pp. 1535-1550, 2005. This article also discloses methods for segmentation that may be used for demarcating a tumor tissue. In radiooncology, segmentation and registering of image data are known.